Small- and large-sized iron(II, III) oxide nanoparticles for surface-assisted laser desorption/ionization mass spectrometry of small biomolecules.

Common surface-assisted laser desorption/ionization (SALDI) surfaces are functionalized to improve mass spectrometric detection. Such surfaces are selective to certain group(s) of compounds. The application of universal and sensitive SALDI surfaces with appropriate size/surface area is paramount. In this study, two different sizes/surface areas of Fe3 O4 are compared as SALDI surfaces. For accurate surface area comparisons, the physical properties of the Fe3 O4 nanoparticles used as SALDI surfaces were determined using scanning electron microscopy, X-ray diffractometry, and N2 Brunauer-Emmet-Teller adsorption techniques. SALDI mass spectrometry (MS) data were acquired using a time-of-flight (TOF) mass spectrometer operated in the linear mode and equipped with a 50-Hz pulsed nitrogen laser (at 337 nm). Small biomolecules (adenosine, glucose, sucrose, tryptophan, and tripeptide) and a real sample (human serum) were analyzed. The average sizes/specific surface areas of the SALDI surfaces of the small- and large-sized Fe3 O4 nanoparticles were ~21 nm/~82 m2 /g and ~39 nm/~38 m2 /g, respectively. An overall ~2.0-fold enhancement in signal-to-noise ratios was observed for the ionic species of the analyzed biomolecules in SALDI-MS using small-sized Fe3 O4 in comparison to large-sized Fe3 O4 nanoparticles. MS sensitivity from adenosine calibration curves (concentration between 0.05 and 10.0 mM) was ~2.0-fold higher for small-sized than large-sized Fe3 O4 nanoparticles as SALDI surfaces. We have shown that transition-metal oxides such as Fe3 O4 nanoparticles are suitable and efficient surfaces for SALDI-TOF-MS analysis of small biomolecules. We observed improvement in signal-to-noise ratios and detection sensitivity for the analyzed samples from SALDI surfaces using small-sized (possessing larger surface area) than large-sized Fe3 O4 nanoparticles.